Auto immune disorders or immune complex diseases, typified by rheumatoid arthritis, systemic lupus erythematosis (SLE), and lupus nephritis, are, as the names imply, disorders caused by a complex of various antigens and antibodies, that is, an immune complex. The mechanisms of immune complex diseases are so complicated that many points still remain for clarification; however, the diseses are considered generally to proceed as follows:
When tissues are damaged by bacterial or viaral infection, antibodies are produced against newly formed autoantigens or virally infected cells and the antibodies react with the corresponding antigens to form immune complexes. Since these immune complexes activate the complement system and platelets, vasoactive substances such as histamine and serotonin are released and the permeability of the blood vessels is increased. Then, the immune complexes in circulation enter the vessel wall whose permeabiity has been increased and deposit along the basement membrane. Polymorphonuclear leukocytes gather at the immune complex-deposited site due to the leukocyte chemotactic factors which have been formed by the reaction of the complement to the deposited immune complexes. The polymorphonuclear leukocytes, reacting with the immune complexes, release various tissue-damaging substances such as cathepsins D and E, collagenase, elastase and permeability factors, and these substances eventually damage the tissue. In patients with immune complex diseases such as SLE, levels of the complement in the serum are generally low and aggravation of the disease conditions is closely correlated with the decrease of the complement levels. This decline is thought to be due to plentiful consumption of the complement at the site of the reaction between antigens and antibodies taking place such as in the kidneys and blood vessels. Further, the immune complexes also are related to blood coagulation systems, and it is believed that the immune complexes cause serious symptoms through diverse mechanisms, for example by acceleration of fibrinoid deposition on the damaged tissues.
Currently in use for the treatment of these immune complex diseases are physiotherapy and plasma-replacement therapy in addition to medical treatment with steroids, immunosuppressive agents, anti-inflammatory agents and so forth. In particular, plasma-replacement therapy is one of the most reliable treating methods for removing immune complex, a pathogenic factor, but the advantages of this method are not being sufficiently utilized because of the difficulty in securing the supply of plasma necessary for use in the plasma-replacement.